1. Field of the Invention
The present invention relates generally to the field of automated sensing systems and methods. More specifically, the present invention is directed to systems and methods for detecting the presence and/or absence of a substance (solid, liquid, gas, or mixture thereof), utilizing an RF energy emitter and RF energy receiver/detector for determining whether a substance is present within a defined physical space between the RF energy emitter and RF energy receiver/detector.
2. Description of Related Art
A wide variety of conventional systems and methods are available for determining whether a solid or liquid is present within a specified physical space utilizing an RF emitter and RF energy detector.
In US patent number 2004/0119637 Angel et al. describe a sensor that utilizes changes in the impedance of a transmission line to determine whether an ink cartridge has run out of ink.
U.S. Pat. No. 6,691,563 by Trabelsi et al. gives a method using a calibration equation to calculate the degree of moisture in particulate matter. In their method, the degree of RF signal attenuation is measured when passed through particulate matter and this is one of the factors used to derive moisture content.
Both U.S. Pat. Nos. 4,727,311 and 4,674,325 by Walker and Kiyobe et al. respectively transmit a microwave signal via horns to measure moisture.
U.S. Pat. No. 7,068,050 by Steele et al. measure the degree of attenuation of signal transmitted by a near field effect to determine the moisture content of lumber. This device operates strictly in the near field.